Chromatin Structure and Transcription
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What are epigenetic changes?
Changes to chromatin structure which affect gene expression but do not alter DNA sequences and are reversible
How long can epigentic modifications last?
They may persist for the life of a cell or organism Or they may be erased in the germ line
Who described the epigentic landscape?
Conrad Waddingtion in 1940
What is the epigenetic landscape?
Describes how different cell fates during development are the end result of distinct journeys
What are the building blocks of chromatin?
Nucleosomes
How can nucleosomes be modified and what is the effect of this?
Covalently modified These structural changes to chromatin affect gene transcription
What part of the nucleosomes are covalently modified?
The tails of core histones
How many histone tails are there and why?
There are 8 as each histone is made up of 8 histone proteins
What is the role of the tails>
They help pack the nucleosomes together in the 30nm fibre
Models of nucleosomes are based on what?
Experimental evidence that histones aid this X ray crystal structure of the nucleosome shows tails contacting the histone core of the adjacent nucleosome
Give examples of the covalent modifications added to core histones with chromatin
Acetlyation of lysines in core histone N terminal tails Methylation of lysines and arginenes in core histone n terminal tails
What two chemical modifications can both occur on lysine?
methylation acetlyation These chemical modifications compete with each other
Give the list of prominent types of covalent amino acid side chain modifications
Acetyl lysine Monomethyl lysine Dimethyl lysine Trimethyl lysine
If lysine is acetlyated it can not be what?
Methylated
What are HATs and HMTs
Histone acetyl transferases Histone methyl transferases
Lysine acetylation has what effect on gene expression?
Active genes
Lysine methylation has what effect on genes?
Can be both inactive and active